This invention relates to information reproducing apparatus which employs a video disk or the like, and more particularly, to optical information reproducing apparatus which effects the reproduction of information with a plurality of light beams of different wavelengths.
Heretofore, information reproducing apparatus employing, for example, a video disk as an information recording medium has utilized a He - Ne laser as a light source for the reproduction of information from the disk. However, the He - Ne laser itself is quite expensive, so that the cost of the whole apparatus becomes unbearably high. Another disadvantage of such equipment is that, since the length of the laser is as great as 20 - 30 cm, it is virtually impossible to produce a compact form of this apparatus. A further disadvantage is that, since the information detection from the disk, the tracking and the auto-focusing are conducted with a single laser beam, the construction of the combination of optical systems for these operations becomes very complicated.
In order to solve the problems inherent in the prior art device, it has been proposed to adopt a semiconductor laser instead of the He - Ne laser. The mere substitution of the semiconductor laser for the He - Ne laser, however, results in the following problems. First of all, the laser power provided by the semiconductor laser is insufficient. In the second place, the disadvantage of the complicated optical system is not eliminated by the mere substitution of lasers.
There has been further prior art apparatus of the specified type, which is so constructed that an identical part of the information recording medium, or parts very close to each other, is illuminated with at least two light beams and the light reflected from the illuminated part or parts or transmitted therethrough is split into respective light beams for information detection, tracking and auto-focusing, the light beams being received by independent detectors.